Actuators provided with a motor and a strain wave gearing as a reduction mechanism are well-known. There are numerous control systems for actuators having this configuration to which is applied a semi-closed control system for performing positioning control of a load shaft for transmitting reduced output rotation of the strain wave gearing to a load side, using only motor shaft information. However, there is a problem with semi-closed control systems in that vibration is generated in the load shaft by a nonlinear element present in the strain wave gearing, and positioning accuracy inevitably declines. The present inventors have therefore proposed methods for compensating for angular transmission error using a model that has been analyzed, modeled, and constructed with regard to angular transmission error (Patent Documents 1 to 4).
In contrast, there have also been proposed full-closed control systems for controlling a load shaft position using information from encoders attached to each of a motor shaft and a load shaft in an actuator provided with a strain wave gearing. The present inventors have proposed a method for preventing degradation in position control performance of the load shaft caused by a nonlinear characteristic of the strain wave gearing in such a control device (Patent Document 5).